Chain saw



FIG. 1 is a perspective view of my new design for a chain saw;

FIG. 2 is a top view thereof;

FIG. 3 is a rear view of FIG. 1;

FIG. 4 is a bottom view of FIG. 1;

FIG. 5 is a right side view of FIG. 1; and,

FIG. 6 is a left side view of FIG. 1.

The broken lines shown in the drawings form no part of the claimed design. 

The ornamental design for a chain saw, as shown and described. 